Remove "Moved Document from ..." notice in Phriction

Summary:
Ref T13410. See PHI1431. Currently, when you move a document in Phriction, the target shows a "This document was moved from ..." banner until it is edited.

This banner isn't particularly useful, and it's distracting and it isn't obvious how to dismiss it, and making a trivial edit to dismiss it is awkward.

This information is also already available in the transaction log.

Just remove this banner since it doesn't really serve any clear purpose.

Test Plan:

• Moved a page in Phriction, then loaded the destination page. Before change: header banner. After change: nothing.
• Viewed a normal (non-moved) page, saw normal behavior.
• Reviewed transactions, saw "Moved from ..." in the timeline.

Maniphest Tasks: T13410

Differential Revision: https://secure.phabricator.com/D20800